Metal-on-metal joint arthroplasty: potential lifetime longevity

We have studied a historical group of patients who underwent metal-on-metal hip arthroplasty more than 30 years ago. Those retaining their original metal-on-metal articulation (average follow-up 33 years) had an average Harris Hip Score of 75 (range 53-93) and an average Musculoskeletal Tumour Outcome Score of 75 (range 63-90). Those that have been revised (at an average of 22 years) maintain good functional outcome. The original implant is still in situ in five of the 11 survivors (follow-up 26-38 years). Retrieval analysis using a Mitutoya form tracer and an electron microscope demonstrated the self-polishing capacity of the metal-on-metal articulation. The surface roughness (Ra) of the worn articulating surface (Ra 0.05 mm) was smoother than that of the original unworn surface (Ra 0.32 mm). We believe our case series highlights the potential longevity of metal-on-metal articulation.